The present invention relates generally to environmental control systems for aircraft, and more particularly to a compact device for removing suspended water, snow and ice from the air supply system of an aircraft.
Aircraft have environmental control systems (ECS) which may include an air supply for cabin air or avionics cooling which is connected to the compressor region of the engine or auxiliary power unit (APU) of the aircraft. Bleed air at high temperature and pressure is conducted from the engine or APU, passed through a series of heat exchangers and valves, and expanded through an air turbine to near ambient pressure to achieve the desired cooling. The cooled air at the turbine outlet normally is below about 32.degree. F., is slightly above normal cabin pressure, and is saturated with water, a large portion of which condenses into liquid and/or freezes. The fog or snow so produced is highly undesirable in the air fed to the cabin or avionics of the aircraft.
Conventional ECS systems of aircraft operate at an air flow rate of about 25 lb/min, turbine inlet pressure of about 45-60 psia and inlet temperature of about 150.degree. F., and turbine outlet pressure of about 1.1 psig. Fogging or icing occurs at the turbine outlet when the ambient air has a moisture content of at least 90 grains of water per 1 b of air, which translates to ambient conditions where the air temperature is 60.degree. F. at any humidity level or is higher than 60 .degree. F. at high relative humidity. The foregoing analysis translates to a maximum needed ice removal rate from the ECS turbine outlet of about 0.44 ft.sup.3 /hr.
In existing ECS systems, cold air at the turbine outlet is mixed with additional warm bleed air to raise the air stream temperature above freezing, which severely reduces the overall cooling capacity of the ECS. Mixing bleed air with the turbine outlet air can result in loss of cooling capacity as high as 50%. Further. depending on the relative humidity of the bleed air, mixing bleed air with cold turbine outlet air can cause moisture to precipitate from the bleed air, which adds to the fogging problem. Using additional bleed air represents parasitic loss from the engine or APU and induces malfunctions and corrosion in avionics equipment. Therefore, a low pressure, low temperature water separator for removing condensed/frozen moisture at the outlet of the turbine is desirable.
The present invention solves or reduces in critical importance the problems with the prior art and meets the desired criteria just stated by providing a low temperature, low pressure separator downstream of the expansion turbine for removing water, snow or ice from the air supply of the ECS of an aircraft. The invention comprises in a representative embodiment a plurality of spaced screens mounted within a tubular housing, and upon which condensed or frozen water is captured by impaction. The captured water is removed from the screens by a wiper or brush. The screens may be rotatable within the chamber against a stationary wiper or brush, or may be stationary and the wiper or brush made to rotate against the screens. The water so removed is discharged into a container for recovery or into a drain for dispoal. A plurality of cascaded screens may be included to attain a desired efficiency or capacity of the separator. The invention may be constructed as a compact unit of less than about one cubic foot and may operate reliably at minimal pressure drop of two psi or less and collection efficiency greater than 90%. The separator may be installed as an integral part of an ECS on new aircraft or retrofitted to existing aircraft. Considering the undesirable alternative loss of cooling power suffered in existing ECS systems where bleed air is used to warm the snow or fog, a small pressure drop across the separator is acceptable while providing significant gain in ECS cooling capacity.
It is therefore a principal object of the invention to provide a device for removing condensed or frozen water from an air stream.
It is a further object of the invention to provide a compact device for removing condensed or frozen water from an air supply to an aircraft cabin and avionics.
It is a further object of the invention to provide a device for removing condensed or frozen water from an air stream using screens.
It is a further object of the invention to provide a compact reliable device for removing water particles from a high-speed gaseous stream with low pressure differential across the device.
These and other objects of the invention will become apparent as the detailed description of representative embodiments proceeds.